UK Equine Scientists Investigating Cause of Mystery Mare Disease

Equine scientists at the University of Kentucky are working with farm managers and horse industry leaders to rapidly diagnose and control a serious problem affecting the equine industry. An unusually high number of late-term abortions and early fetal deaths have been submitted recently to the UK Livestock Disease Diagnostic Center in Lexington.

"Investigation is underway, and we are pulling more and more people in, not just from our own equine research faculty but also from other UK departments and from the horse industry itself," said David Powell, disease researcher with UK's Maxwell Gluck Equine Research Center.

Horse owners are reporting two problems. One problem is a significant number of late-term abortions and a number of foals being born weak and surviving only a few days. Symptoms in mares include non-production of milk, difficulty giving birth, and stillborn fetuses. The cause is unknown.

Another problem relates to an increased number of mares determined to be pregnant at about 40 days, but then experiencing early fetal loss. Affected mares seem normal during manual pregnancy examinations, but during ultrasound tests an abnormal fluid is seen around the fetus. UK researchers and veterinarians believe this problem may be related to the first, however the cause is also unknown.

The late-term abortions and early fetal losses are widespread and not restricted to Thoroughbreds.

"This is problem involves many breeds and farms," said Powell. "The problem does not appear to be contagious -- that is, spread by one horse coming into contact with another horse.

Horse owners are being urged to report late-term abortions or other similar problems. Veterinarians are being advised to consider ultrasounding mares at 60-65 days of gestation. If the mare aborts, fetal tissue and a serum sample should be submitted to the UK Livestock Disease Diagnostic Center.

As part of the collaborative investigation now underway, a questionnaire was sent on May 7 to horse farm managers.

"We're sending this questionnaire out by way of the Thoroughbred Farm Managers Club," said Powell. "It's going out to all farms in order that we can get a better handle on the true incidence of this condition."

Powell said a fact sheet is being prepared for widespread distribution throughout the state. Information also will be available on the UK College of Agriculture's web site:, click news & events.

"We're assembling a team that includes equine practitioners, farm managers, nutritionists, soil and pasture specialists, state agencies and others to evaluate the problem," said Powell. "Until we get some more factual information it's difficult to say exactly what the degree of severity is, but at this point we can say we're dealing with an extremely serious problem."

Interview with Dr. David Powell, equine epidemiologist, UK Gluck Equine Research Center

When was the problem with late-term abortions and early fetal loss in horses first reported?

We first became aware of the problem around the middle of last week on May the 2nd when my colleague Dr. Roberta Dwyer and I visited farms that were experiencing these problems.

What do we know at this point about possible causes?

At this stage we do not have a definite diagnosis as to what is causing either of these problems but we are undertaking a very thorough investigation.

What have we ruled out as the cause?

We are looking at possible infectious causes and other possible causes involving pasture. At this stage we have ruled out a number of viral causes, and others will hopefully be eliminated over the next few days.

What are initial steps being taken to diagnose and control the problem?

At the end of last week we set up various groups of individuals both within the university and outside the university to investigate specific aspects of this problem. They have been out in the field taking samples which have been sent to various laboratories - both the UK Diagnostic Lab and other laboratories in Kentucky and other parts of the United States - to identify whatever might be causing this problem. There's an extensive team of individuals investigating this problem at the present time.

Will affected mares be able to produce foals in the future?

Based on past experience of this kind of problem, at this stage we would feel reasonably confident that mares that are bred back would get in foal, but it's still early days to make too dogmatic a statement.

What are the potential economic impacts?

We don't know the true incidence of this condition but we will have precise figures before the end of this week. lit is therefore unclear at present as to what the economic losses are going to be. I think at this stage we appreciate the losses are going to be serious if we think in terms of lost stud fees based on the mares that have lost their foals or fetuses.

What should veterinarians and horse owners be doing?

Unfortunately at this time we cannot give precise advise until we have a definitive diagnosis. We are suggesting to farm owners not to graze their mares on really lush pastures, and to mow those pastures. Hopefully we will be able to provide them with much more specific as the information on what is causing this problem becomes available.

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